Phased array amplifier linearization

ABSTRACT

Apparatus and methods provide predistortion for a phased array. Radio frequency (RF) sample signals from phased array elements are provided along return paths and are combined by a hardware RF combiner. Phase shifters are adjusted such that the RF sample signals are phase-aligned when combined. Adaptive adjustment of predistortion for the amplifiers of the phased array can be based on a signal derived from the combined RF sample signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending application titled ANTENNAARRAY CALIBRATION SYSTEMS AND METHODS, Ser. No. 15/611,289, filed onJun. 1, 2017, the disclosure of which is hereby incorporated byreference in its entirety herein. This application is also related toapplication titled SPATIAL DIGITAL PRE-DISTORTION, Ser. No. 15/372,723filed Dec. 8, 2016, the disclosure of which is hereby incorporated byreference in its entirety herein.

This application is a divisional application of U.S. patent applicationSer. No. 15/801,232, filed Nov. 1, 2017, the disclosure of which ishereby incorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the invention generally relate to antennas, and inparticular, to predistortion in connection with phased-array antennas.

Description of the Related Art

Radio frequency (RF) power amplifiers are used in a variety ofapplications, such as telecommunications, radars and the like. When asignal is amplified by an RF power amplifier, the amplified signal canbecome distorted due to non-linearities in RF power amplification. Anupconversion process can also result in non-linearities. The presence ofdistortion can cause problems such as intermodulation distortion,out-of-band emissions, and interference.

One technique to linearize an RF power amplifier is by predistortion.With predistortion, the input signal to the RF power amplifier ispredistorted in a manner that is complementary to the distortion addedby the RF power amplifier to reduce the resulting distortion in theoutput of the RF power amplifier. Such techniques can also be applied tolinearize the combination of an upconverter and RF power amplifier.

However, conventional predistortion techniques cannot be used withanalog beamformers. What is needed is a technique to apply predistortionto the phased array amplifier of an analog beamformer.

SUMMARY OF THE DISCLOSURE

One embodiment includes an apparatus for radio frequency (RF)linearization of multiple amplifiers of a phased array, wherein theapparatus includes: a plurality of return paths configured to carry atleast RF sample signals of a plurality of RF power amplifiers; ahardware RF power combiner configured to combine the RF sample signalsto generate a combined signal; a plurality of return-side phase shiftersconfigured to adjust a phase shift of the RF sample signals such thatthe RF sample signals are phase aligned at the hardware RF powercombiner; and a predistorter configured to predistort an input signal togenerate a predistorted signal and configured to adapt predistortioncoefficients for predistortion based at least partly on observations ofa signal derived from the combined signal.

One embodiment includes a method of linearization of multiple amplifiersof a phased array, wherein the method includes: phase shifting radiofrequency (RF) sample signals of a plurality of RF power amplifiers suchthat the RF sample signals are phase aligned at a hardware RF powercombiner; combining the RF sample signals the hardware RF power combinerto generate a combined signal; and predistorting an input signal with apredistorter to generate a predistorted signal, wherein predistortioncoefficients are based at least partly on comparisons between portionsof the input signal and corresponding portions of a signal derived fromthe combined signal.

One embodiment includes a phased array element for a phased array,wherein the phased array element includes: a switch for switching anantenna element between either a transmit side or a receive side fortime-division duplex operation; and a return path separate from atransmit path, wherein the return path is configured to provide a radiofrequency (RF) sample of a transmitted signal, wherein the return pathfurther comprises a phase shifter configured to adjust a phase of the RFsample.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings and the associated description herein are provided toillustrate specific embodiments of the invention and are not intended tobe limiting.

FIG. 1A is a schematic block diagram of a symmetric routing schematicfor a 4-by-4 antenna array according to an embodiment.

FIG. 1B is a schematic block diagram of an asymmetric routing schematicfor a 2-by-8 antenna array according to another embodiment.

FIG. 2A is an illustration of a horizontal wavefront according to anembodiment.

FIG. 2B is an illustration of an angled wavefront according to anembodiment.

FIG. 2C is a schematic block diagram of a series of transceiversaccording to an embodiment.

FIG. 2D is an illustration of a planar array and an associatedelectromagnetic pattern according to an embodiment.

FIG. 3A is a schematic block diagram of a probe with a power detectordisposed between two antenna elements according to an embodiment.

FIG. 3B-1 and 3B-2 are flow diagrams for calibration using a probe witha power detector disposed between two antenna elements according to anembodiment.

FIG. 3C is a schematic block diagram of a probe with a mixer disposedbetween two antenna elements according to an embodiment.

FIG. 3D is a flow diagram for calibration using a probe with a mixerdisposed between two antenna elements according to an embodiment.

FIG. 4 is a schematic block diagram of probes disposed between fourantenna elements according to an embodiment.

FIG. 5A is a schematic block diagram of probes disposed between an arrayof three by four antenna elements according to an embodiment.

FIG. 5B is a flow diagram for calibration using probes disposed betweenan array of three by four antenna elements according to an embodiment.

FIG. 6A is a schematic block diagram of a probe with an RF power sourcedisposed between two antenna elements according to an embodiment.

FIG. 6B is a flow diagram for calibration using a probe with an RF powersource disposed between two antenna elements according to an embodiment.

FIG. 7 illustrates a phased array with predistortion.

FIG. 8A illustrates an embodiment of a phased array element.

FIG. 8B illustrates another embodiment of a phased array element.

FIG. 8C illustrates another embodiment of a phased array element.

FIG. 9 illustrates a method of arranging signal for collection of datafor the determination of predistortion coefficients.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

An antenna array can enable a beamformer to steer an electromagneticradiation pattern in a particular direction, which generates a main beamin that direction and side lobes in other directions. The main beam ofthe radiation pattern is generated based on constructive inference ofthe signals based on the transmitted signals' phases. Furthermore, theamplitudes of the antenna elements determine side-lobe levels. Abeamformer can generate desired antenna patterns by, for example,providing phase shifter settings for the antenna elements. However, overtime, the amplitudes of signals and the relative phases among theantenna elements can drift from the values set when the antenna wasoriginally calibrated. The drift can cause the antenna pattern todegrade, which can, for example, reduce the gain in a main lobe. Thus,what is needed is a way to accurately measure and control the phase andamplitude of antenna elements in an array system even after an antennaarray has been fielded. Furthermore, the calibration process itself canbe relatively labor intensive, time consuming, and costly. Thus, thereis a need for a method of calibration without the need for expensivetest equipment and facilities and having to relocate the antenna to aparticular location. These disclosed techniques are also applicable tothe manufacturing test environment and can be used to speed production,thus lowering costs. In one embodiment, the calibration data is used bythe beamformer and combined with other data, such as pre-calculated orpre-stored antenna pattern data, to generate appropriate settings forbeamforming.

The present disclosure enables an antenna array to perform calibrationusing relative measurements of phase and/or absolute measurements ofamplitude. A probe is placed between antenna elements and the phaseand/or amplitude of the antenna elements are measured. Then, the phaseor amplitude can be assessed to determine adjustments that are made tothe transmitter, receiver, or transceiver connected to the antennaelements. In some embodiments, the antenna elements can transmitsignals, and the phase of one or more antenna elements can be adjusteduntil a relatively high or maximum and/or relatively low or minimumpower level is reached. Upon determining a relatively high or maximumpower level, the phase adjuster or shifter values are recorded as thosecorresponding to in phase, and for a relatively low or minimum powerlevel, the phase values are recorded as 180 degrees out of phase.Although embodiments describe the use of a probe, it is appreciated thatother structures (e.g. conductors) that can transmit and/or receivesignals may also be used (e.g. slots, monopole, small patches, othercoupling structures, etc).

In some embodiments, the probe should be disposed symmetrically betweenthe antenna elements. For example, if there are two antenna elements,the probe can be placed in between the two antenna elements. In anotherexample, if there are four antenna elements, the probe can be placeddiagonally between the four antenna elements equidistant from each ofthe four antenna elements. Placing the probe symmetrically betweenantenna elements reduces or eliminates the possible variation that mayoccur in the propagation of the radiation pattern to or from the probeand the antenna elements.

In some embodiments, the antenna elements can be used to transmitsignals to the probe, the probe receiving the transmitted signals. Theprobe can detect power (e.g. by using a power detector) or detect bothpower and phase (e.g. by using a mixer). Alternatively, the probe can beused as a transmitter, transmitting a signal to the antenna elements,where the antenna elements receive the transmitted signal.

Using a single probe to calibrate multiple antennas is advantageous.Having a single probe that may be used to transmit to the antennaelements and/or receive signals from antenna elements may itselfintroduce variation to the signal. However, since the same probe andcomponents connected to the probe (e.g. mixer) are used to measure thesignal, there is advantageously no part-to-part or channel-to-channelvariation with the disclosed techniques. For example, the probe and thecomponents connected to the probe will introduce the same variation to asignal received at the probe from a first and second antenna element.

By contrast, couplers used to measure phase and amplitude of a signal tocalibrate antenna elements would introduce variation. A separate couplerwould be connected to the transmit path of each antenna element. Then,the signal would travel along the signal route to components connectedto each coupler. The routing path from each coupler to their associatedconnected components would introduce channel to channel variation. Eachcoupler may be connected to its own set of components, which despitepossibly being of the same kind of components, the components themselvesintroduce part to part variability. Furthermore, the couplers themselvesuse additional hardware such as switches. The couplers themselves, oftenmade of metallic substances, may interfere with the radiation signalmaking it harder to obtain higher isolation between the antennaelements. These drawbacks are reduced or eliminated by embodiments ofthe invention.

Embodiments of the present disclosure including using a probe disposedbetween antenna elements are advantageous in that the probes can be usedto calibrate the array based on near field radiation measurements. Thus,the array can be calibrated without the need for far field measurements.Typically, electromagnetic anechoic chambers, (also called echo-freechambers) can be used to simulate an open space situation. The time andspace in these chambers may be difficult to schedule, may be expensive,and time consuming. However, embodiments of the present disclosure avoidthe need of having to place the antenna in an anechoic chamber becausenear-field measurements are used instead of far-field measurements.Furthermore, anechoic chambers may be practical for initial calibration,but not for later calibration. Some embodiments of the antenna array ofthe present disclosure may be calibrated repeatedly and at the field.The probes can be permanently placed in between antenna elements. Theantenna array may be configured to allow temporary installment of theprobes in between the antenna elements as well. Some embodiments of thenear-field calibration of the present disclosure may also be helpful forsmall signal difference.

The calibration method and system can be used to calibrate arrays ofdifferent sizes. For example, the system can calibrate a planar array bycalibrating a first set of antenna elements (or calibration group) thatare equidistant to one probe, then calibrating a second set of antennaelements equidistant to another probe where the first and second set ofantenna elements share at least one antenna element. Then, the sharedantenna element can be used as a reference point to calibrate the otherantenna elements.

Although the disclosure may discuss certain embodiments with the probeas the receiver and the antenna elements as the transmitter, it isunderstood that the probe can act as a transmitter and the antennaelements as a receiver, and vice versa.

FIG. 1A is a schematic block diagram of a symmetric routing schematic100 according to an embodiment. The symmetric routing schematic 100includes antenna elements, 102A, 102B, 102C, 102N, 102E, 102F, 102G,102H, 1021, 102J, 102K, 102L, 102M, 102N, 1020, and 102P (collectivelyreferred to herein as 102). The symmetric routing schematic 100 alsoincludes a chip 104A, 104E, 1041, and 104M (collectively referred toherein as 104). The symmetric routing schematic 100 includes atransceiver 110 and routing paths 106A, 106B, 106C, 106D, 106E, 106F,106G, 106H, 1061, 106J, 106K, 106L, 106M, 106N, 1060, 106P, 108A, 108E,1081, and 108M (collectively referred to herein as 106) from thetransceiver 110 to the antenna elements 102.

FIG. 1A refers to a symmetric routing schematic 100 for a 4-by-4 antennaarray. The schematic refers to symmetric routing because the routes onthe routing paths 106 from the transceiver 110 to the antenna elements102 are of the same distance. For example, the routing path fromtransceiver 110 to antenna element 102A is a combination of the routingpaths 108A and 106A, while the routing path from transceiver 110 toantenna element 102B is a combination of the routing paths 108A and106B. The routing paths are generated to minimize variation in thedistance the signal travels from the transceiver 110 to the antennaelement 102. This type of configuration helps to mitigate the variationthat may cause difficulties in calibration due to different lengths ofrouting paths the signal travels from the transceiver 110 to the antennaelement 102.

The antenna elements 102 may be radiating elements or passive elements.For example, the antenna elements 102 may include dipoles, open-endedwaveguides, slotted waveguides, microstrip antennas, and the like.Although some embodiments illustrate a certain number of antennaelements 102, it is appreciated that the some embodiments may beimplemented on an array of two or more antenna elements.

FIG. 1B is a schematic block diagram of an asymmetric routing schematic150 for a 2-by-4 antenna array according to another embodiment. Theasymmetric routing schematic 150 includes antenna elements 152A, 152B,152C, 152D, 152E, 152F, 152G, and 152H (collectively referred to hereinas 152). The asymmetric routing schematic 150 also includes a chip 154.The asymmetric routing schematic 150 includes routing paths 156A, 156B,156C, and 156D (collectively referred to herein as 156) from the chip154 to the antenna elements 152. FIG. 1B is directed to asymmetricrouting because the routing paths 156 from the chip 154 to the antennaelements 152 are different in lengths. Thus, the phase and amplitudevaries differently from channel to channel. For example, the transmittedsignal at the antenna element 152 may be different from element toelement even though the same signal was transmitted from the chip 154.In some embodiments, the received signal at the antenna elements 152 maybe the same, but different when received at the chip 154 as a result ofthe different lengths of the routing paths 156.

FIG. 2A is an illustration of a horizontal wavefront 200 according to anembodiment. Each antenna element 102 may radiate in a sphericalradiation pattern. However, the radiation patterns collectively generatea horizontal wavefront 204. The illustration 200 includes antennaelements 102A, 102B, 102C, 102N, 102M-1 and 102M. The antenna elements102A, 102B, 102C, and 102N may be arranged linearly, where the elementsare arranged on a straight line in a single dimension. In thisconfiguration, the beam may be steered in one plane. The antennaelements may also be arranged planarly, arranged on a plane in twodimensions (N direction and M direction). In this planar configuration,the beam may be steered in two planes. The antenna elements may also bedistributed on a non-planar surface. The planar array may berectangular, square, circular, or the like. It is appreciated that theantenna may be arranged in other configurations, shapes, dimensions,sizes, types, other systems that can implement an antenna array, and thelike. The illustration of the horizontal wavefront 200 shows each of theantenna elements 102 transmitting a signal 202A, 202B, 202C, 202N,202M-1, and 202M (collectively referred to herein as 202) creating ahorizontal wavefront 204. The illustration of FIG. 2A illustrates anantenna array creating a main beam that points upward, as shown by thehorizontal wavefront 204. The phases from the antenna elements 102 areconstructively interfering in the upward direction.

FIG. 2B is an illustration of an angled wavefront 220 according to anembodiment. The illustration of the angled wavefront 220 includesantenna elements 102A, 102B, 102C, 102N, 102M-1 and 102M. The antennaelements may be arranged similarly to that described for FIG. 2A. Theillustration of an angled wavefront 220 shows the antenna elements 102transmitting a signal 222A, 222B, 222C, 222N, 222M-1, and 222M(collectively referred to herein as 222) creating a wavefront 224 thatpropagates at an angle, different from the direction of the wavefront204 in FIG. 2A. The phases of the signals 222 are constructivelyinterfering in the direction that the angled wavefront 220 is traveling(e.g. up-right direction). Here, each of the phases of the antennaelements 102 may be shifted by the same degree to constructivelyinterfere in a particular direction.

The antenna elements 102 can be spaced apart equidistant from oneanother. In some embodiments, the antenna elements 102 are spaced atdifferent distances from each other, but with a probe equidistant fromat least two antenna elements 102.

Although the disclosure may discuss certain embodiments as one type ofantenna array, it is understood that the embodiments may be implementedon different types of antenna arrays, such as time domain beamformers,frequency domain beamformers, dynamic antenna arrays, active antennaarrays, passive antenna arrays, and the like.

FIG. 2C is a schematic block diagram of a series of transceivers 240A,240B, 240N (collectively referred to herein as 240) according to anembodiment. In some embodiments, a single transceiver 240 feeds to asingle antenna element 102. However, it is appreciated that a singletransceiver 240 may feed to multiple antenna elements 102, or a singleantenna element 102 may be connected to a plurality of transceivers 240.Furthermore, it is appreciated that the antenna element 102 may belinked to a receiver and/or a transmitter.

In some embodiments, the transceiver 240 may include a switch 242A,242B, 242N (collectively referred to herein as 242) to switch the pathfrom the antenna element 102 to the receiver or the transmitter path.The transceiver 240 includes another switch 248A, 248B, 248N(collectively referred to herein as 248) that switches the path from thesignal processor (not shown) to the receiver or the transmitter path.The transmitter path has a phase adjuster 244A, 244B, 244N (collectivelyreferred to herein as 244) and a variable gain amplifier 246A, 246B,246N (collectively referred to herein as 246). The phase adjuster 244adjusts the phase of the transmitted signal at the antenna element 102and the variable gain amplifier 246 adjusts the amplitude of thetransmitted signal at the antenna element 102. Although the embodimentsdescribe the transceiver 240 including a phase adjuster 244 and avariable gain amplifier 246, other components can be used to adjust themagnitude of the signal and/or the phase of the signal. Furthermore,although a switch is shown to switch from the transmitter path to thereceive path, other components can be used, such as a duplexer.

The receiver path may also have a phase adjuster 250A, 250B, 250N(collectively referred to herein as 250), and a variable gain amplifier252A, 252B, 252N (collectively referred to herein as 252). The phaseadjuster 250 and the variable gain amplifier 252 can be used to adjustthe received signal from the antenna element 102 before going to thesignal processor (not shown).

FIG. 2D is an illustration of a planar phased array 260 and anassociated electromagnetic pattern according to an embodiment. FIG. 2Dincludes antenna elements 102A, 102B, 102N, 102M-1, and 102M. FIG. 2Dalso includes a beam pattern with a main beam 262, and side lobes 264A,264B, 264C. The antenna elements 102 are transmitting a signal where thephase of the signal is constructively interfering in the direction ofthe main beam 262. The precision of the amplitude of the antennaelements 102 controls the side-lobe levels. For example, the moreuniform the amplitudes of the transmitted signals from the antennaelements 102 are, the lower the side lobe levels will be. The antennaelements 102 may be disposed on a single die, or multiple dies.

FIG. 3A is a schematic block diagram 300 of a probe 310A with a powerdetector 312A disposed between two antenna elements 102A, 102B accordingto an embodiment. In this block diagram 300, the probe is disposedequidistant between the two antenna elements 102A, 102B. The probe 310Amay be a slot, a probe, a coupling element, any component that can beused to detect signals, or the like. The probe can be used as atransmitter.

FIG. 3B-1 and 3B-2 is a flow diagram for calibration using a probe witha power detector disposed between two antenna elements according to anembodiment.

FIG. 3B-1 illustrates a flow diagram 320 for measuring and comparing allpower levels for the two antenna elements 102A, 102B. At block 322, thetransmitter tied to the antenna element 102B is turned off. At block324, a signal is transmitted from the first antenna element 102A. Asignal is generated from the mixer 302A, amplified by the variable gainamplifier 246A, shifted in phase by the phase adjuster 244A, andtransmitted from the antenna element 102A. At block 326, the probe 310Adetects the transmitted signal from the antenna element 102A and thepower detector 312A detects power values of the detected signal. Atblock 327, the system can determine whether all power and/or phaselevels are measured. If yes, then the system can continue to block 328.If not, then the power and/or phase can be adjusted in block 323, andproceed back to block 324. For example, a combination of each powerlevel and each phase level can be measured. In some embodiments, thephase and amplitude are decoupled such that each power level can bemeasured and each phase level measured independently without having tomeasure every combination of each power level and each phase level.

At block 328, the transmitter tied to the antenna element 102A is turnedoff. At block 330, a signal is transmitted from the second antennaelement 102B. A signal is generated from the mixer 302B, amplified bythe variable gain amplifier 246B, shifted in phase by the phase adjuster244B, and transmitted from the antenna element 102B. At block 332, theprobe 310A detects the transmitted signal from the antenna element 102Band the power detector 312A detects power values of the detected signal.

At block 334, once the detected signals from the transmitted signals ofantenna elements 102A and 102B are stored, the power values are comparedto calibrate the transmitter connected to the antenna element 102Arelative to the transmitter connected to the antenna element 102B,and/or vice versa. The power values are calibrated by adjusting the gainof the variable gain amplifier 246A and/or 246B. In some embodiments,the calibration is performed during, before, or after other blocks inFIG. 3B. After comparing power values to calibrate the antenna elementsat block 334, the flow can continue to FIG. 3B-2.

FIG. 3B-2 illustrates a flow diagram 321 for calibrating the phase forthe two antenna elements 102A, 102B. At block 325, a signal of the samepower level is transmitted from both antenna elements 102A, 102B. Thiscan be achieved using data obtained from the steps in FIG. 3B-1. Atblock 329, the phase of the first antenna element 102A is changed. Thenat block 335, the total power can be measured by a power detector 312A.The system determines whether the maximum power level is measured atblock 336. If not, then the system continues to change the phase of thefirst antenna element 102A and continues the flow diagram from block329. If the maximum power level is measured at block 336, then the phasecan be determined to be in an in-phase condition. The phases thatprovide the maximum power level at block 336 is recorded for the antennaelements at block 337.

At block 338, the phase of the first antenna element 102A is changed,and at block 339, the total power is measured using the power detector312A. At block 340, the system determines whether the minimum powerlevel is measured. If not, then the phase of the first antenna element102A is changed and the flowchart continues from block 338. If theminimum power level is measured, then the system records the phasecalibration information for the antenna elements at block 341. This canbe considered a 180 degrees out of phase condition.

FIG. 3C is a schematic block diagram 330 of a probe 310A with a mixer342A disposed between two antenna elements 102A, 102B according to anembodiment. The probe 310A may be disposed equidistant from the antennaelements 102A and 102B. The probe 310A is connected to the mixer 342A.

FIG. 3D is a flow diagram 360 for calibration using a probe with a mixerdisposed between two antenna elements according to an embodiment. Themixer can be used to measure phase and/or amplitude. At block 362, thetransmitter connected to antenna element 102B is turned off. At block364, a signal is generated from the mixer 302A, amplified by thevariable gain amplifier 246A, phase shifted by the phase adjuster 244A,and transmitted by the antenna element 102A. At block 366, the probe310A detects the transmitted signal and using the mixer, the signalprocessor measures and records the amplitude and phase values. At block367, the system can determine whether all power and/or phase levels havebeen measured. If yes, then the system can proceed to block 368. If no,then the system can adjust power and/or phase levels in block 363, andreturn to block 324.

At block 368, the transmitter connected to the antenna element 102A isturned off. At block 370, a signal is generated from the mixer 302B,amplified by the variable gain amplifier 246B, shifted in phase by thephase adjuster 244B, and transmitted by the antenna element 102B. Atblock 372, the probe 310A detects the signal, the mixer mixes thesignal, and the signal processor measures and records the phase andamplitude values. At block 373, the system can determine whether allpower and/or phase levels have been measured. If yes, then the systemcan proceed to block 374. If no, then the system can adjust power and/orphase levels in block 369, and return to block 370.

At block 374, based on a comparison between the amplitudes of thesignals transmitted by the antenna element 102A and 102B, the variablegain amplifiers 246A, 246B are adjusted such that the amplitudes arecalibrated to transmit substantially the same power based on the samesignal generated. Furthermore, based on a correlation between the phasesof the signals transmitted by the antenna element 102A and 102B, thephase adjusters 244A and 244B are adjusted such that the phases arecalibrated to transmit at substantially the same phase for the samegenerated signal.

The values of the variable gain amplifier 246A, 246B and/or the phaseadjusters 244A, 244B may be controlled using a digital command sentthrough the beam steering interface, such as the beam steering chip orthe signal processor. The phase adjuster may be an n-bit phase adjusterproviding control of the phase in a total of a particular number ofphase degrees. Thus, the calibration process may be calibrated to be thestate that allows for the closest phase value. In some embodiments, thecalibration is performed during, before, or after other blocks in FIG.3D.

FIG. 4 is a schematic block diagram 400 of probes 310A, 310B, 310Cdisposed between four antenna elements 102A, 102B, 102C, 102N accordingto an embodiment. In the block diagram 400, probe 310A is disposedequidistant from antenna element 102A and antenna element 102B. Theprobe 310B is disposed equidistant from antenna element 102B and antennaelement 102C. The probe 310C is disposed equidistant from antennaelement 102C and antenna element 102N. The antenna elements 102A, 102B,102C, and 102N are disposed linearly.

In this embodiment, antenna elements 102A and 102B are calibrated first.The transmitters connected to the antenna elements 102B, 102C, and 102Nare turned off. The mixer 302A generates a signal, the signal shifted inphase by the phase adjuster 244A, the signal amplified by a variablegain amplifier 246A, and transmitted from the antenna element 102A. Theprobe 310A receives the signal. Next, the antenna 102B transmits asignal that the same probe 310A detects. In this embodiment, the probe310A is connected to a power detector 312A. Antenna elements 102A and102B are calibrated similar to the process described in FIG. 3A.However, the probe 310A may be connected to mixers and may be calibratedsimilar to the process described in FIG. 3B. Other ways of calibrationare possible. For example, other components may be connected to theprobe 310A to measure phase and/or amplitude. Furthermore, other methodsof calibration may be used using relative measurements of phase and/oramplitude.

Next, antenna elements 102B and 102C are calibrated. Then, 102C and 102Nare calibrated. In this embodiment, the calibration occurs serially.However, calibration may occur in different time steps. For example,when antenna element 102B is transmitting a signal to calibrate withantenna 102A, not only can probe 310A be detecting the signal, but alsoprobe 310B may detect the signal. Thus, while antenna elements 102A and102B are being calibrated, the calibration between antenna elements 102Band 102C can begin in parallel. In this embodiment, neighboring antennaelements are being calibrated. However, it is appreciated that any setof antenna elements that are equidistant from the probe can becalibrated. For example, the first and fourth antenna element 102A, 102Ncan be calibrated with a probe 310B between the second and third antennaelement 102B, 102C.

FIG. 5A is a schematic block diagram of probes disposed between an arrayof three by four antenna elements according to an embodiment. The probes310A, 310B, 310C . . . 310M (collectively referred to herein as 310) aredisposed symmetrically between a set of four antenna elements 102. Inthis embodiment, the probe 310 is equidistant from each antenna element102 in the set of four antenna elements. However, it is appreciated thatthe probe 310 may be placed at some distance that is equidistant from atleast two antenna elements 102.

FIG. 5B is a flow diagram for calibration using probes disposed betweenan array of three by four antenna elements according to an embodiment.

At block 522, all transmitters connected to all antenna elements 102 areturned off. At block 524, the first set of four antenna elements iscalibrated together. Then, the first antenna element 102A transmits asignal. The probe 310A receives this signal, measures the power usingthe power detector 312A, and records the power. This is repeated for theother three antenna elements 102 that are equidistant from the firstprobe 310A. Then, the gain of each antenna element 102 within the set offour antenna elements is adjusted to be calibrated in relation to oneanother. Then, all four antenna elements 102 transmit a signal, thephase adjusted, and the phase recorded to identify the phaseconfigurations that provide maximized power (e.g. the phase values areequal). The same test is performed for when the power is minimized (e.g.phases are 180 degrees apart). Calibration can be performed in a similarmanner to that described in FIG. 3A, 3B, and other ways described inthis disclosure.

Although the disclosure may discuss certain embodiments as calibratingfour antennas at once, it is understood that the embodiments may beimplemented using a different number of transmitters, antenna elements,probes, and the like. For example, the power can be calibrated for fourantenna elements at once (e.g. once power is recorded for four antennaelements, the gain for each of the four antenna elements can be adjustedto meet a reference gain value), while the phase can be calibrated inpairs (e.g. calibrate antenna elements 102A and 102B first, thencalibrate antenna elements 102A and 102M-1 next).

After the antenna elements 102 within the set of four antenna elementshave been calibrated in reference to one another, the calibrationprocedure may calibrate the next set of four antenna elements 102.Antenna elements except for the antenna elements in the next set areturned off at block 526. At block 528, an antenna element that is inboth the first and second set is identified. Then at block 530, the nextset of antenna elements are calibrated with the identified antennaelement as a reference. The next set of four antenna elements 102 may beequidistant from the next probe 310B. The same or a differentcalibration method may be used for the next set of four antenna elements102. After the sets of antenna elements 102 across the row of elementsare calculated, the process can be repeated for the following column ofa set of four antenna elements 102. For example, after the set ofantenna elements 102 have been calibrated using the probes 310A, 310B,and 310C, then the next set of four antenna elements 102 to becalibrated may be those that are equidistant from the probe 310M.

Once the power values are calibrated, the transmitter connected to theantenna element 102A and the transmitter connected to the antennaelement 102B are turned on. Based on the power calibration, the antennaelements 102A and 102B transmit signals at substantially the same powerlevel. Adjust one or both of the phase adjuster 244A or 244B. The probe310A will receive both signals from antenna elements 102A and 102B anddetect the power values at the power detector 312A. When the power ismaximized, the phase adjuster 244A and 244B are aligned (e.g. the phasevalues are equal). When the power is minimized, the phase adjuster 244Aand 244B are opposite (e.g. phase of one equals the phase of the otherplus 180 degrees). Using this relative relationship, the system cancalibrate the phase of one antenna element relative to the other antennaelement.

FIG. 6A is a schematic block diagram of a probe 310A with an RF powersource 610 disposed between two antenna elements 102A, 102B according toan embodiment. In this block diagram 600, the probe 310A is disposedequidistant between the two antenna elements 102A, 102B. The probe 310Amay transmit a signal for the antenna elements 102A and 102B to receive.

FIG. 6B is a flow diagram for calibration using a probe with an RF powersource disposed between two antenna elements according to an embodiment.At block 622, the probe 310A is a radiating element that transmits asignal. The probe 310A can be connected to an RF power source 610. Atblock 624, the antenna elements 102A, 102B receives the signaltransmitted from the probe 310A. The antenna elements 102A, 102B can beconnected to a phase adjuster 604A and 604B, the variable gain amplifier606A, 606B, and an I/Q mixer 602A, 602B. The antenna elements 102A, 102Breceives the signal and detects the phase and amplitude using the I/Qmixer 602A, 602B. At block 626, the antenna elements are calibratedbased on a comparison of the detected phase and amplitude measurements.

FIG. 7 illustrates a phased array with predistortion linearization. Inone embodiment, the phased array corresponds to an analog phased arrayor to a hybrid phased array and is used in connection with atime-division duplex (TDD) communication system, such as a mobile phonebase station. Other systems, such as radar systems, are also applicable.As will be explained in greater detail later in connection with FIGS.8A-8C, the phased array elements 702 a-702 n can include phase shiftersand variable gain amplifiers to adjust a pattern or “beam” of the phasedarray for both transmitting and receiving. In some embodiments, theamount of phase shift and gain adjustment to be applied to each phasedarray element for a desired pattern can be determined by the techniquesdescribed earlier in connection with FIG. 1A to 6B. However, othertechniques can alternatively be used.

A predistorter 704 includes a digital signal processor (DSP) 706 and anadaptive control 708. An input signal V_(S)(t) is provided as an inputto the DSP 706. For example, the input signal V_(S)(t) can be generatedby a modulator of a modem and correspond to a baseband complexmodulation envelope. The DSP 706 can perform predistortion on the inputsignal V_(S)(t) on a sample-by-sample basis to generate a predistorteddrive signal V_(P)(t) that complements the nonlinearities collectivelyintroduced by the RF power amplifiers of the phased array elements 702a-702 n. In the illustrated embodiment, the same predistortion providedby the predistorter 704 is applied to multiple or to all RF poweramplifiers of the phased array elements 702 a-702 n of the phased array.

A wide variety of algorithms can be used for predistortion. Moreover,the DSP 706 can correspond to a wide variety of signal processingcircuits, such as, but not limited to, a finite impulse response (FIR)filter, a lookup table, or the like. The manner by which the DSP 706predistorts the input signal V_(S)(t) is determined by the particularpredistortion algorithm being implemented and the coefficients withinthe DSP 706. The adaptive control 708 can compare samples of the inputsignal V_(S)(t) with corresponding samples of a digital feedback signalV_(DR)(t) to determine appropriate coefficients for predistortion thatare applied by the DSP 706. These appropriate coefficients can vary withdifferent amplifiers, over time, over temperature, over different drivelevels, over varying beam pattern, or the like, and can be adaptivelyadjusted as needed by the adaptive control 708. For discussions onpredistortion and adaptive adjustment, see, for example, NAGATA, Y.,Linear Amplification Technique for Digital Mobile Communications, IEEEVehicular Technology Conference (1989), pgs. 159-164; and CAVERS, J. K.,Amplifier Linearization Using A Digital Predistorter With FastAdaptation And Low Memory Requirements, IEEE Transactions on VehicularTechnology, Vol. 39, No. 4, pp. 374-383, November 1990.

Adaptive adjustment and the collection of RF samples for adaptiveadjustment need not be performed continuously and can instead beperformed sporadically, such as periodically, or in response to changes,such as changes to beam angle/antenna pattern/gain/power levels.

The DSP 706 can be implemented in hardware, such as in an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or the like. Portions of the adaptive control 708 can beimplemented in software/firmware by a processor executingmachine-readable instructions for the particular predistortionalgorithm. The computations performed by the adaptive control 708 do notneed to be performed in real time and can be performed using data storedin and retrieved from a memory device.

A digital-to-analog converter (DAC) 710 converts the predistorted drivesignal V_(P)(t) from a digital form to an analog form and provides ananalog predistorted drive signal V_(A)(t) as an input to an upconverter712. The upconverter 712 converts the analog predistorted drive signalV_(A)(t) to an upconverted signal V_(U)(t). In the illustratedembodiment, the analog predistorted drive signal V_(A)(t) is a basebandsignal, and the upconverted signal V_(U)(t) is a higher-frequencysignal, and can be, for example, radio frequency, microwave frequency,millimeter wave (RF/MW/mmw). In the context of this disclosure, the termradio frequency (RF) will include, but is not limited to, microwave andmillimeter wave frequencies. In one example, the upconverter 712 cancorrespond to a quadrature upconverter. Other types of upconverters canbe used. The upconverter 712 can include, for example, a mixer, afilter, and a variable gain amplifier.

The upconverted signal V_(U)(t) is provided as an input to a powerdivider 714, which can include one or more Wilkinson power dividers. Incontrast to conventional TDD systems, in some embodiments, the powerdivider 714 is dedicated to the transmit/forward path and is not usedfor the receive/return path. The power divider 714 provides the multiplephased array elements 702 a-702 n with the same predistorted signal as adrive signal.

The phased array elements 702 a-702 n include the RF power amplifiers tobe linearized as well as other components. The number of phased arrayelements 702 a-702 n in the phased array can vary in a very broad range.While not restricted to a power of 2, a number that is a power of 2 canbe easier to implement. In one example, the number of phased arrayelements 702 a-702 n is in a range between 16 and 1024. In someembodiments, each of the phased array elements 702 a-702 n can bemanufactured to be identical to each other, but can vary duringoperation with different phase shifter and or gain/power settings. Thephased array elements 702 a-702 n can have a transmit terminal T, areceive/return terminal R, and an antenna element terminal T. Incontrast to a conventional phased array element for a TDD system, thetransmit and receive/return paths in some embodiments of the inventioncan be separated or dedicated. This advantageously provides relativelylarge cost and size improvements over systems in which each RF amplifierof a phased array has its own predistortion linearization. For clarity,other terminals such as power and control terminals are not shown.Various embodiments for the phased array elements 702 a-702 n will bedescribed in greater detail later in connection with FIGS. 8A-8C.

In the illustrated embodiment, the return/receive paths are the samepaths and are separate from the forward/transmit paths. In someembodiments, each receive path adjusts the phase of its received signal,such that all received signals are added in-phase. Amplitude adjustmentin the receive path is also possible, to compensate for path mismatches,if any. A hardware RF power combiner 716 combines the signals from thereturn/receive paths to generate a combined signal V_(C)(t), which isprovided as an input to a downconverter 718. During a transmit phase,the return/receive paths can carry RF sample signals. During a receivephase, the return/receive paths can carry received signals, such assignals transmitted by mobile phones. In some embodiments, the hardwareRF power combiner 716 can include one or more Wilkinson combiners. Thehardware RF power combiner 716 does not correspond to a multiplexer.

The downconverter 718 converts the combined signal V_(C)(t), which is anRF signal, to a downconverted signal V_(D)(t), which can be a basebandor intermediate frequency signal. The downconverter 718 can include amixer and a filter, and in some embodiments, can include additionalamplifiers. The downconverted signal V_(D)(t) is provided as an input toan analog-to-digital converter (ADC) 720, which converts thedownconverted signal V_(D)(t) to a digital downconverted signalV_(DR)(t).

When the phased array is transmitting, selected samples of the digitaldownconverted signal V_(DR)(t) can be collected for analysis foradaptive adjustment of predistortion. When the phased array isreceiving, the digital downconverted signal V_(DR)(t) can, for example,be provided as an input to a demodulator of the modem (not shown) togenerate received data.

The adaptive control 708 can compare samples of the input signalV_(S)(t) with corresponding samples of the digital downconverted signalV_(DR)(t) to estimate the predistortion coefficients. For example, thesamples from the input signal V_(S)(t) can be scaled, rotated, anddelayed to align with the samples of the digital downconverted signalV_(DR)(t). In one example, an adaptive algorithm can tune itspredistortion coefficients to minimize the total error (such asmean-squared error) between the input signal V_(S)(t) and the digitaldownconverted signal V_(DR)(t).

FIGS. 8A-8C illustrate various embodiments of phased array elements 802,822, 842. Other variations are possible. These phased array elements802, 822, 842 can be used for any of the phased array elements 702 a-702n described earlier in connection with FIG. 7. To avoid repetition ofdescription, components having the same or similar function may bereferenced by the same reference number.

In the embodiment illustrated in FIG. 8A, the transmit path and thereceive/return path are separate. In a TDD system, transmitting andreceiving occur at different times. When transmitting, thereturn/receive path can be used for providing RF samples of thetransmitted signal. When receiving, the return/receive path is used toprovide received signals. The phased array element 802 includes atransmit-side phase shifter 804, a variable gain RF power amplifier 806,a leaky switch 808, a low-noise amplifier (LNA) 810, and a return-sidephase shifter 812. The amount of phase shift provided by thetransmit-side phase shifter 804 and the amount of gain of the variablegain RF power amplifier 806 are determined based on the antenna patternor beamforming desired.

When transmitting, a relatively small amount of the transmitted powercan be leaked across the leaky switch 808 from the transmit side to thereturn/receive side for collection of RF samples for adaptiveadjustment. Ordinarily, the leaky switch 808 selects either the transmitside or the return/receive side for the antenna element. An appropriateamount of leakage between the transmit side and the return/receive sidecan be specified and deliberately introduced for the leaky switch 808.The amount of leakage that will be applicable can vary in a very broadrange and can vary with an amount of gain provided by the LNA 810. Thisleaked power provides the return/receive side with an RF sample of thetransmitted signal.

The LNA 810 can be present in the return/receive path for reception ofsignals from other sources, such as mobile phones, but is not needed forthe RF sampling of the transmitted signal. During RF sampling, the gainof the LNAs 810 of the plurality of phased array elements 802 can be thesame. During operation, the return-side phase shifter 812 can havedifferent settings depending on whether the return/receive paths arebeing used for collection of RF samples for adaptive adjustment ofpredistortion or are being used for receiving.

When the return/receive paths are being used for collection of RFsamples, the return-side phase shifters should be adjusted such that thereturn path signals are aligned in phase at the hardware RF powercombiner 716 (FIG. 7). In some embodiments, this can mean that thereturn-side phase shifter 812 effectively performs the opposite phaseshift to the phase shift of the transmit-side phase shifter 804. It willbe understood that there can be variations in path lengths that can needto be taken into account by additional offsets. These variations can bedetermined during a manufacturing or calibration process and stored in alookup table. When the return/receive paths are being used forreceiving, the return-side phase shifters 812 can be adjusted toimplement the desired antenna pattern.

In the embodiment illustrated in FIG. 8B, transmit path andreceive/return path are again separate or dedicated paths. The phasedarray element 822 includes a transmit-side phase shifter 804, a variablegain RF power amplifier 806, a directional coupler 824, a switch 826, alow-noise amplifier (LNA) 810, and a return-side phase shifter 812. In aTDD system, the switch 826 selects the transmit side for the antennaelement when transmitting, and the switch 826 selects the receive sidefor the antenna element when receiving.

When transmitting, a relatively small amount of the transmitted power(known as an RF sample) is coupled via the directional coupler 824 fromthe transmit side to the return/receive side for collection of RFsamples for adaptive adjustment. The coupling factor is not critical.For example, the coupling factor can be −10 decibels (dB), −20 dB, orthe like. Other amounts are applicable for the coupling factor and willbe readily determined by one of ordinary skill in the art. However, insome embodiments, the coupling factor is about the same for thedirectional couplers 824 of the phased array. The RF samples from thecoupled output can be provided to the return/receive path ahead of orbehind the LNA 810, but should be provided ahead of the return-sidephase shifter 812. For example, switches can be used to provide the RFsamples to the desired points in the signal path.

As described earlier in connection with FIG. 8A, when the return/receivepaths are being used for collection of RF samples, the return-side phaseshifters 812 should be adjusted such that the return path signals arealigned in phase at the hardware RF power combiner 716 (FIG. 7). Whenthe return/receive paths are being used for receiving, the return-sidephase shifters 812 can be adjusted to implement the desired antennapattern.

In the embodiment illustrated in FIG. 8C, transmit path and the receivepath can be the same, and a dedicated return path can provide RF samplesfor adaptive adjustment. The phased array element 842 includes atransmit-side phase shifter 804, a variable gain RF power amplifier 806,a directional coupler 824, a switch 826, a low-noise amplifier (LNA)810, a return-side phase shifter 844, and a receive-path phase shifter846.

In the embodiment illustrated in FIG. 8C, the transmit and receiveoperations can be similar to those found in conventional phased arrayelements. The power divider 714 can provide combining functions for thereceive path, and components such as the downconverter 718 and ADC 720can be duplicated for the receive path and the return path, as thereceive path and the return path are separate in FIG. 8C.

The directional coupler 824 provides the RF samples to the return-sidephase shifter 844, which can be adjusted such that the return pathsignals are aligned in phase at the hardware RF power combiner 716 (FIG.7). The gain of the LNA 810 and the phase of the receive-path phaseshifter 846 can be adjusted based on the desired antenna pattern orbeamforming.

FIG. 9 illustrates a method of arranging signal for collection of datafor the determination of predistortion coefficients. The process adjuststhe phase of the RF sample signals such that the RF sample signals arephase aligned 902 at the hardware RF power combiner 716 (FIG. 7). Thephase alignment can be accomplished by providing phase adjustments tothe phase shifters 812, 844 (FIGS. 8A-8C). These phase-aligned RF samplesignals are combined 904 in the hardware RF power combiner 716 of thephased array to generate a combined signal. The adaptive adjustmentalgorithm can then determine 906 the appropriate predistortioncoefficients to use based on comparisons between portions of the inputsignal and corresponding portions of a signal derived from the combinedsignal, such as from corresponding portions of a downconverted anddigitally converted version of the combined signal.

Any of the principles and advantages discussed herein can be implementedin connection with any other systems, apparatus, or methods that benefitcould from any of the teachings herein. For instance, any of theprinciples and advantages discussed herein can be implemented inconnection with any devices with a need to adjust the amplitude or phaseof a phased array.

Aspects of this disclosure can be implemented in various electronicdevices. For instance, one or more of the above phased array embodimentscan implemented in accordance with any of the principles and advantagesdiscussed herein can be included in various electronic devices. Examplesof the electronic devices can include, but are not limited to, cellphone base stations, radar systems, radar detectors, consumer electronicproducts, parts of the consumer electronic products such assemiconductor die and/or packaged modules, electronic test equipment,etc. Examples of the electronic devices can also include communicationnetworks. The consumer electronic products can include, but are notlimited to, a phone such as a smart phone, a laptop computer, a tabletcomputer, a wearable computing device such as a smart watch or an earpiece, an automobile, a camcorder, a camera, a digital camera, aportable memory chip, a washer, a dryer, a washer/dryer, a copier, afacsimile machine, a scanner, a multifunctional peripheral device, awireless access point, a router, etc. Further, the electronic device caninclude unfinished products, including those for industrial and/ormedical applications.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including,” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The words “coupled” or“connected”, as generally used herein, refer to two or more elementsthat may be either directly connected, or connected by way of one ormore intermediate elements. Thus, although the various schematics shownin the figures depict example arrangements of elements and components,additional intervening elements, devices, features, or components may bepresent in an actual embodiment (assuming that the functionality of thedepicted circuits is not adversely affected). Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the Detailed Description of Certain Embodiments using thesingular or plural number may also include the plural or singularnumber, respectively. The words “or” in reference to a list of two ormore items, is intended to cover all of the following interpretations ofthe word: any of the items in the list, all of the items in the list,and any combination of the items in the list. All numerical values ordistances provided herein are intended to include similar values withina measurement error.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, systems, andmethods described herein may be embodied in a variety of other forms.Furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

1.-6. (canceled)
 7. An apparatus for radio frequency (RF) linearizationof multiple amplifiers of a phased array, the apparatus comprising: aplurality of return paths configured to carry at least RF sample signalsof a plurality of RF power amplifiers; a switch configured toelectrically connect an antenna element to a transmit path in a firststate and to electrically connect the antenna element to a return pathof the return paths in a second state, wherein the switch is configuredto leak a sufficient amount of power from the transmit path to thereturn path such that the return path receives enough transmit powerrepresented in an RF sample of the RF samples for adaptive adjustment ofpredistortion; a hardware RF power combiner configured to combine the RFsample signals to generate a combined signal; a plurality of return-sidephase shifters configured to adjust a phase shift of the RF samplesignals such that the RF sample signals are phase aligned at thehardware RF power combiner; and a predistorter configured to predistortan input signal to generate a predistorted signal and configured toadapt predistortion coefficients for predistortion based at least partlyon observations of a signal derived from the combined signal.
 8. Theapparatus of claim 7, wherein the plurality of return-side phaseshifters are configured to effectively perform an opposite phase shiftto phase shifts of transmit-side phase shifters.
 9. The apparatus ofclaim 7, wherein the return-side phase shifters are disposed in thereturn paths.
 10. The apparatus of claim 7, wherein the RF poweramplifiers are further configured to receive the same predistortedsignal.
 11. The apparatus of claim 7, further comprising one or moreprocessors configured to determine new predistortion coefficients inresponse to a change in a beamforming pattern of the phased array. 12.The apparatus of claim 7, wherein the predistorter comprises a digitalsignal processer and an adaptive control.
 13. The apparatus of claim 12,wherein the digital signal processer comprises a lookup table.
 14. Anapparatus for radio frequency (RF) linearization of multiple amplifiersof a phased array, the apparatus comprising: a plurality of return pathsconfigured to carry at least RF sample signals of a plurality of RFpower amplifiers; means for providing RF samples to the plurality ofreturn paths; a hardware RF power combiner configured to combine the RFsample signals to generate a combined signal; a plurality of return-sidephase shifters configured to adjust a phase shift of the RF samplesignals such that the RF sample signals are phase aligned at thehardware RF power combiner; and a predistorter configured to predistortan input signal to generate a predistorted signal and configured toadapt predistortion coefficients for predistortion based at least partlyon observations of a signal derived from the combined signal.
 15. Theapparatus of claim 14, wherein the means for providing the RF samplescomprises a switch configured to leak power from a transmit path to areturn path of the plurality of return paths.
 16. The apparatus of claim15, wherein the switch is configured to selectively electrically connecteither the transmit path or a receive path to an antenna element. 17.The apparatus of claim 16, wherein the receive path is the return path.18. The apparatus of claim 14, wherein the plurality of return-sidephase shifters are configured to effectively perform an opposite phaseshift to phase shifts of transmit-side phase shifters.
 19. The apparatusof claim 14, wherein the return-side phase shifters are disposed in thereturn paths.
 20. A method for radio frequency (RF) linearization ofmultiple amplifiers in a phased array, the method comprising: providingRF samples to respective return paths using switches, wherein a switchof the switches leaks a sufficient amount of power from a transmit pathto a return path of the return paths such that the return path receivesenough transmit power represented in an RF sample of the RF samples foradaptive adjustment of predistortion; phase shifting the RF samples suchthat phase shifted RF samples are phase aligned at an RF power combiner;combining, with the RF power combiner, the phase shifted RF samplesignals to generate a combined signal; and predistorting an input signalusing predistortion coefficients to generate a predistorted signal,wherein the predistortion coefficients are based at least partly onobservations of a signal derived from the combined signal.
 21. Themethod of claim 20, wherein said phase shifting effectively performs anopposite phase shift to phase shifts of transmit-side phase shifters.22. The method of claim 20, further comprising applying the samepredistorted signal to a plurality of RF power amplifiers of the phasedarray.
 23. The method of claim 20, further comprising determining newpredistortion coefficients in response to a change in a beamformingpattern of the phased array.
 24. The method of claim 20, furthercomprising: downconverting the combined signal with a downconverter to adownconverted signal; and converting the downconverted signal with ananalog-to-digital converter to generate a feedback signal, wherein thefeedback signal comprises the signal derived from the combined signal.25. The method of claim 20, wherein said predistorting the input signalis performed on a sample-by-sample basis to generate a predistorteddrive signal that complements the nonlinearities collectively introducedby a plurality of RF power amplifiers.
 26. The method of claim 20,wherein said predistorting is performed using data stored and retrievedfrom a memory device.